<meta charset="utf-8">
(#) Composable functions should emit XOR return

!!! ERROR: Composable functions should emit XOR return
   This is an error.

Id
:   `ComposeContentEmitterReturningValues`
Summary
:   Composable functions should emit XOR return
Severity
:   Error
Category
:   Productivity
Platform
:   Any
Vendor
:   slack
Identifier
:   com.slack.lint.compose:compose-lints
Feedback
:   https://github.com/slackhq/compose-lints/issues
Min
:   Lint 8.7+
Compiled
:   Lint 8.7+
Artifact
:   [com.slack.lint.compose:compose-lint-checks](com_slack_lint_compose_compose-lint-checks.md.html)
Since
:   1.0.0
Affects
:   Kotlin and Java files and test sources
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://github.com/slackhq/compose-lints/tree/main/compose-lint-checks/src/main/java/slack/lint/compose/ContentEmitterReturningValuesDetector.kt)
Tests
:   [Source Code](https://github.com/slackhq/compose-lints/tree/main/compose-lint-checks/src/test/java/slack/lint/compose/ContentEmitterReturningValuesDetectorTest.kt)
Copyright Year
:   2023

Composable functions should either emit content into the composition or
return a value, but not both. If a composable should offer additional
control surfaces to its caller, those control surfaces or callbacks
should be provided as parameters to the composable function by the
caller. See
https://slackhq.github.io/compose-lints/rules/#do-not-emit-content-and-return-a-result
for more information.

(##) Options

You can configure this lint checks using the following options:

(###) content-emitters

A comma-separated list of known content-emitting composables.
This property should define a comma-separated list of known content-emitting composables.


Example `lint.xml`:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~xml linenumbers
&lt;lint&gt;
    &lt;issue id="ComposeContentEmitterReturningValues"&gt;
        &lt;option name="content-emitters" value="some string" /&gt;
    &lt;/issue&gt;
&lt;/lint&gt;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/test.kt:3:Error: Composable functions should either emit content
into the composition or return a value, but not both.If a composable
should offer additional control surfaces to its caller, those control
surfaces or callbacks should be provided as parameters to the composable
function by the caller.See
https://slackhq.github.io/compose-lints/rules/#do-not-emit-content-and-return-a-result
for more information. [ComposeContentEmitterReturningValues]
@Composable
^
src/test.kt:8:Error: Composable functions should either emit content
into the composition or return a value, but not both.If a composable
should offer additional control surfaces to its caller, those control
surfaces or callbacks should be provided as parameters to the composable
function by the caller.See
https://slackhq.github.io/compose-lints/rules/#do-not-emit-content-and-return-a-result
for more information. [ComposeContentEmitterReturningValues]
@Composable
^
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`src/test.kt`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers
import androidx.compose.runtime.Composable

@Composable
fun Something() {
    Text("Hi")
    Text("Hola")
}
@Composable
fun Something() {
    Spacer16()
    Text("Hola")
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://github.com/slackhq/compose-lints/tree/main/compose-lint-checks/src/test/java/slack/lint/compose/ContentEmitterReturningValuesDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `ContentEmitterReturningValuesDetector.errors when a Composable function has more than one UI emitter at the top level`.
To report a problem with this extracted sample, visit
https://github.com/slackhq/compose-lints/issues.

(##) Including

!!!
   This is not a built-in check. To include it, add the below dependency
   to your project. This lint check is included in the lint documentation,
   but the Android team may or may not agree with its recommendations.

```
// build.gradle.kts
lintChecks("com.slack.lint.compose:compose-lint-checks:1.4.2")

// build.gradle
lintChecks 'com.slack.lint.compose:compose-lint-checks:1.4.2'

// build.gradle.kts with version catalogs:
lintChecks(libs.compose.lint.checks)

# libs.versions.toml
[versions]
compose-lint-checks = "1.4.2"
[libraries]
# For clarity and text wrapping purposes the following declaration is
# shown split up across lines, but in TOML it needs to be on a single
# line (see https://github.com/toml-lang/toml/issues/516) so adjust
# when pasting into libs.versions.toml:
compose-lint-checks = {
    module = "com.slack.lint.compose:compose-lint-checks",
    version.ref = "compose-lint-checks"
}
```

1.4.2 is the version this documentation was generated from;
there may be newer versions available.

[Additional details about com.slack.lint.compose:compose-lint-checks](com_slack_lint_compose_compose-lint-checks.md.html).
(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("ComposeContentEmitterReturningValues")
  fun method() {
     problematicStatement()
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("ComposeContentEmitterReturningValues")
  void method() {
     problematicStatement();
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection ComposeContentEmitterReturningValues
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="ComposeContentEmitterReturningValues" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'ComposeContentEmitterReturningValues'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore ComposeContentEmitterReturningValues ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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